Disclosed in JP2009-46093A is an example of a known seat occupancy determining apparatus that includes plural load sensors between a cushion portion of a passenger seat (e.g. a front passenger seat, which will be hereinafter referred to also as a vehicle seat) for the vehicle and a vehicle floor and that detects a seat occupancy state of the vehicle seat (i.e. a seating state of an passenger on the vehicle seat) on the basis of a sum of loads detected by plural load sensors. More specifically, according to the seat occupancy determining apparatus disclosed in JP2009-46093A, a side leg portion is formed at each of four corners at a bottom portion of a seat cushion portion, so that the seat cushion portion is movably engaged with seat rails via the side leg portions. The load sensor is provided at each side leg portion, so that the load sensor detects a load applied to the corresponding side leg portion. The seat occupancy determining apparatus disclosed in JP2009-46093A further includes a seat occupancy determining portion, which detects the seating state of the passenger on the vehicle seat by comparing the sum of the loads detected by plural load sensors with a predetermined threshold value.
The seat occupancy determining apparatus executes various controls. For example, the seat occupancy state of the vehicle seat (i.e. the seating state of the passenger on the vehicle seat) detected by the seat occupancy determining apparatus is used for an actuation control of an air bag. More specifically, for example, in a case where the seat occupancy determining apparatus determines that an adult is seated on the passenger seat for the vehicle, the seat occupancy determining apparatus controls the air bag to be in a fully-deployable state. On the other hand, in a case where the seat occupancy determining apparatus determines that the passenger is not seated on the vehicle seat or in a case where the seating determination apparatus determines that a child is seated on a child seat that is fastened to the vehicle seat, the seat occupancy determining apparatus controls the air bag not to be opened or not to be fully-deployed.
However, the seat occupancy state of the vehicle seat (i.e. the seating state of the passenger on the vehicle seat) may not be properly detected in the case where the seat occupancy state of the vehicle seat is determined only on the basis of the sum of the loads applied thereto. For example, a relatively great load may be temporarily applied to the seat cushion when the child seat is fastened to the vehicle seat by means of a seat belt in order to attach the child seat on the vehicle seat.
In other words, in a case where the child seat is placed on the vehicle seat and a tongue of the seat belt is engaged with a buckle of the seat belt, a relatively great load is likely to temporarily act on the seat cushion via the buckle. In a case where the load applied to the seat cushion becomes equal to or greater than a predetermined threshold value when the tongue and the buckle are engaged, the seat occupancy determining apparatus may mistakenly determine that an adult is seated on the vehicle seat.
The above-mentioned drawback is more likely to occur in a case where the number of load sensors provided at the vehicle seat is reduced in order to reduce manufacturing costs of the vehicle seat. In other words, accurately detecting the seating state of the passenger on the vehicle seat (i.e. the seat occupancy state of the vehicle seat) conflicts with a reduction of the manufacturing costs of the vehicle seat.
A need thus exists to provide a seat occupancy determining apparatus which is not susceptible to the drawback mentioned above.